Why stackless (async/await) for Swift?

[tera]

@AlexanderM

TL;DR: Implementing async/await as sugar over Promises like in JS or Python just leads to a linked list of promises. It's a very simple and straightforward implementation with fantastic backwards compatibility, but it's a pain train of heap allocations and indirection (which is marginally cost in itself, but it prohibits a lot of other optimizations). Coroutine based async/await is much more complicated to implement (but luckily that's done already, great work team!), but better in every other way I can think of.

Not that winning a popularity contest means it's necessarily better, but it's worth noting that C#, Rust and Go have all gone with some flavour of coroutine (stackful or stackless) as their backing primitive for async/await.

Thank you Alexander, I'm quoting you here as it is more appropriate to have it here rather in the topic named "The Swift Postmortem".

Anyone here aware of a good benchmark (or a set of benchmarks) to compare different approaches in this space? I tried the mentioned skynet benchmark but it only touches a fraction of the relevant surface area.